1. Field of the Invention
This invention relates to a method of fabrication used for semiconductor integrated circuit devices, and more specifically to a structure and method for producing integrated circuits with multiple polysilicon wiring layers having an improved contamination guard ring for circuit redundancy applications and laser repair alignment mark applications.
2. Description of Related Art
Integrated circuits often include fusible conductive links that may be rendered non-conductive by running a high current through them. The conductive links can also be rendered nonconductive by applying laser energy with a laser repair machine. A serious disadvantage of such fusible link regions, as well as of alignment mark regions, is that both frequently lower chip yield and reliability by allowing moisture and other contaminates to penetrate to the device regions of the semiconductor circuits.
An important challenge is to improve the reliability of the semiconductor devices surrounding fusible links and alignment mark regions and it has become customary to provide a guard ring of moisture impervious material to surround the region of the fusible link or the region of the alignment mark in order to block the penetration of moisture and other contaminates from reaching the device areas.
For example, U.S. Pat. No. 5,567,643 entitled "Method of Forming Contamination Guard Ring For Semiconductor Integrated Circuit Applications" granted Oct. 22, 1996 to Jin-Yuan Lee et al describes a process of forming a guard ring that uses two water impervious layers; e.g. first and second metal layers bonded to the silicon substrate.
Also, U.S. Pat. No. 5,538,924 entitled "Method of Forming a Moisture Guard Ring For Integrated Circuit Applications" granted Jul. 23, 1996 to Chung-zen Chen shows a guard ring composed of a polysilicon layer and a metal layer and a silicon nitride barrier layer.
And, U.S. Pat. No. 5,444,012 entitled "Method For Manufacturing Semiconductor Integrated Circuit Device Having a Fuse Element" granted Aug. 22, 1995 to Keiichi Fukuda al describes a guard ring composed of three layers of wiring material; i.e. lower TiW, aluminum alloy, and upper TiW. This guard ring is not bonded to the silicon substrate.
Unless the guard ring is bonded to the semiconductor substrate the effectiveness of the guard ring in preventing diffusion of moisture and contaminants from a window in the insulation layers to the device regions is attenuated. Also, it is desirable to be able to form the guard ring without introducing extra processing steps and extra layers into the manufacturing process for the integrated circuit.